This is a special room. Hello I'm tired and is in New York this is an ABC news digital special report an ABC news exclusive today. Several dozen suspected foreign bomb makers including some believed to have targeted American troops in Iraq and Afghanistan. They have mistakenly been allowed to move into the United States as -- refugees. This from FBI agents investigating fingerprints on roadside bomb fragments taken out of -- out. -- chief investigative correspondent Brian Ross reports. The city of Bowling Green, Kentucky seemed far removed from concerns about terrorists. Until the FBI discovered that two al-Qaeda terrorist from Iraq had been resettled here two years ago as refugees. And were caught trying to obtain weapons to be used to kill more Americans. In this video been seen publicly for the first time this morning. I think they wanted to kill Americans but I think they wanted to freedoms that America provided to home. Before coming to Kentucky the two were part of an al-Qaeda connected group that carried out dozens of attacks. And US soldiers in Iraq. -- -- -- -- -- -- -- -- -- -- -- -- -- Including one roadside bomb that killed four members of the Pennsylvania National Guard. I think these you know these two individuals specifically here are innately evil yet the two terrorist Mohammed how Mahdi. And one -- one were able to get true what an ABC news investigation discovered was a flawed US system of background checks even though both men. Had been detained by Iraqi authorities on suspicion of being insurgents. If you're asking mapping -- -- the system -- Otherwise they wouldn't have been here in the first place. A big breakthrough in the case came from this warehouse outside Washington. An FBI repository. Of some 100000. Bombs used against American targets around the world. -- -- the fox campaign. FBI technicians poring over the remnants were able to match the fingerprints on a roadside bomb recovered in Iraq eight years ago with -- -- -- in Kentucky's. -- you can see right here. What was that like when you -- -- made the match the whole team was ecstatic 'cause it was down by defining an analyst takes. And now the FBI says there could be dozens of others in the US whose fingerprints may also be somewhere on the bottom parts store here. We are so currently supporting. Dozens of current -- -- investigations like that. Dozens of cases correct we are looking for prince of people who are in this country this current. -- was ABC news' Brian Ross reporting and we're now joined by ABC news investigative reporter James me good afternoon James Lipton who runs the refugee program that it apparently allow these men into the country. Well it's done with a number of our federal agencies from the State Department. Working with United Nations. To the Department of Homeland Security which owns the US citizenship and immigration services. And they all work with the FBI and the Defense Department. The intelligence community to try to screen refugees who are mostly fleeing persecution and possible death. The case of likened to reporters who helped -- us forces in harm's way. In Iraq and Afghanistan these are people who really a legitimate reason to come here. Unfortunately. A couple years ago. For for a number of years the refugee background checks. Were very deeply flawed that process was not robust enough and a couple of guys got. Into the country were resettled in Bowling Green, Kentucky this relatively small town college town Western Kentucky University. And were living there and the FBI got an intelligence tip that they might be bad characters and have a lot to go on. Began investigating them and then they -- -- soon realizes. These suspects. Begin to brag that they had actually already. Killed American troops -- certainly in Iraq they were posting of this an undercover FBI surveillance tapes and video. As they were involved in a plan that was -- maneuver by a undercover FBI operatives to ship arms -- -- rock course no weapons actually went back to rock. But these two suspects thought -- -- In a machine guns and explosives and stinger anti air missiles. Back to their former com -- Qaeda -- Iraq. But that that those shocking thing was this is the first time. That's the only case -- I'm aware of doing counterterrorism reporting for sixteen years working a little bit counterterrorism myself. You have people who already had American blood on their hands were plotting terrorism while living inside the US homeland. So it's a pretty extraordinary case that they got -- but their backgrounds as as real hard core al-Qaeda Iraq insurgents who would almost certainly killed by their own admission. US troops in harm's way in Iraq. Makes an exceptional case and makes them particularly lethal so they are now in federal prison that both pleaded guilty. Is -- refugee program that allowed them to come and still functioning have there been any changes made it screening process. So the course of an ABC news investigation. We learned in the investigative unit that in fact something that -- not been widely reporter disclosed publicly. The refugee admissions system was shut down completely -- 20114. Half year and during that period nobody can. And a result of that a sort of unfortunate consequence of that. You know essentially are closing the doors to refugees system for six months. -- eleven was -- -- at least one case one Iraqi who assisted US forces in Iraq was assassinated because his refugee application was delayed. But they had to completely overhaul the system and put in place officials said. Many many layers of new security and scrutiny because they admitted they have -- to al-Qaeda terrorists from Iraq. Into the country who have applied as refugees and the background checks completely fail because they came and cleaned according to officials. The back to the specifics of the case when and how -- the FBI decide to target. The Iraqi man at the center of the case while Juan -- what tipped them off. So started with water brought on all one who has now 32 years all of Iraqi from. By sheer rock which is north of Baghdad and he came in as a refugee and was resettled in Bowling Green, Kentucky. And about six months into his and saying their living there. He had you know quit his job and -- gone on welfare was taking public assistance and living in public housing. And the FBI got an intelligence tip that he might be about guys -- -- and it was fairly I think vague. They began to do this investigation they recruited at someone who could be an undercover. Informant who could win the trust of -- Ramadan all one. And that succeeded and then he said you know I have a relative it was her Bowling Green. Is a very experienced I'm paraphrasing what he said this is very experienced -- from Iraq. Named. Mohammed. -- -- -- -- ramadi came into the plot to ship arms back to rock but again the more this sting operation along the more they realize. These -- guys who already -- American blood on their hands they had by their own admission and evidence they discovered in fact all one have been captured by Kurdish forces the 2006 of turnout and had confessed on video. To being a terrorist who targeted American troops. And yet the US did not know about that capture -- been released or confessed on video to being terrorists 2006. And he got into the country anyway. Whether any precedence set with this case and we've certainly heard of enemy combatants before we've heard of homegrown terrorists but this is a slightly different spin on on that. Yeah I mean this was these were people who were enemy combatants and they -- theater but they came to the US homeland. And so while there was a little political storm -- -- at the time about whether there should be sent to Guantanamo Bay and tried in a military commission. You know they were. When they went to the federal court system and in Kentucky Louisville, Kentucky. And they were confronted with be the evidence that the FBI and the just department -- Which was impressive I mean they had videotaped them as we obtained a videotape for if you -- ABC news investigation. -- -- you've been showing. Of them handling these weapons is heavy arms. And they had the evidence that they have been tied to an attack that killed four soldiers from the Pennsylvania National Guard in Iraq in 2005. And they decided to plead guilty all one -- little bit cut forty years. Commodities -- life and super Max prison. I and our do we -- enough they are appealing or there are allowed to appeal. From body appealed his sentence not his admission of guilt and that appeals actually heard on Tuesday of this week. The judges in the case of the six circuit US Court of Appeals were apparently very skeptical. But what this case prompted those -- said was shut down of the refugee admissions system but also. -- of this to scramble the last couple years ago look at other refugees. And the FBI is involved they told us on the record. But they're involved in dozens of counterterrorism investigations where FBI agents around the country have been have -- This FBI lab in Quantico Virginia to look. For fingerprints on IUDs in the FBI has collected the remnants of 100000. IDs. Most of which came from the battlefields of Iraq and Afghanistan. In a program most Americans have never heard. Because they've never publicized. And they are now examining those -- season that backlog which is about half. To try to find fingerprints many other DNA evidence that could you know help identify terrorists here or overseas. Amazing that those tiny fragments thousands of miles away could have such an impact. And launch such an investigation James Michele thank you so much for joining us this afternoon -- -- this has been an ABC news digital special report more on this ABC news exclusive. Al-Qaeda in America tonight on world news and later on Nightline anti Hernandez in New York.

This transcript has been automatically generated and may not be 100% accurate.

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